Jens Axboe wrote: > On Sat, Jun 02 2007, Tejun Heo wrote: >> Hello, >> >> Jens Axboe wrote: >>>> Would that be very different from issuing barrier and not waiting for >>>> its completion? For ATA and SCSI, we'll have to flush write back cache >>>> anyway, so I don't see how we can get performance advantage by >>>> implementing separate WRITE_ORDERED. I think zero-length barrier >>>> (haven't looked at the code yet, still recovering from jet lag :-) can >>>> serve as genuine barrier without the extra write tho. >>> As always, it depends :-) >>> >>> If you are doing pure flush barriers, then there's no difference. Unless >>> you only guarantee ordering wrt previously submitted requests, in which >>> case you can eliminate the post flush. >>> >>> If you are doing ordered tags, then just setting the ordered bit is >>> enough. That is different from the barrier in that we don't need a flush >>> of FUA bit set. >> Hmmm... I'm feeling dense. Zero-length barrier also requires only one >> flush to separate requests before and after it (haven't looked at the >> code yet, will soon). Can you enlighten me? > > Yeah, that's what the zero-length barrier implementation I posted does. > Not sure if you have a question beyond that, if so fire away :-) I thought you were talking about adding BIO_RW_ORDERED instead of exposing zero length BIO_RW_BARRIER. Sorry about the confusion. :-) -- tejun -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
